Cathode organization



April 6, 1937. Q J VON wEDEL 2,075,876

CATHODE ORGAN I ZAT ION Original Filed Dec. 28, 1927 INVENTOR 634m J Rhf m/v W505:

ATTORNEY Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE CATHODEORGANIZATION Application December 28, 1927, Serial No. 243,042 RenewedJanuary 22, 1931 27 Claims.

The present invention relates generally to cathode organizations fordischarge tubes, and more particularly to cathode organizations adaptedto have the necessary heat for electron emission generated byalternating current. It contemplates in particular the so-calledindirectly heated type cathode.

One object of the invention is to provide a cathode organization havingspecial provision for rendering ineffective in large measure thealternating current field effects which tend to create hum producingdisturbances in the operation of discharge tubes as radio and likedetectors and amplifiers. Another object is the provision of specialfeatures permitting the use of currents at high potentials for cathodeheating, as from the usual 110 volt house lighting system.

A further object is the inclusion of features permitting the use ofcurrent at the higher voltages in so-called gas filled tubes whereheretofore this has not been possible on account of the close spacingrequired of the parts of the tube subjected to diiferences of potentialsufficient to produce discharges across these short paths in the gasfilling.

In the indirect method of heating a cathode for electron emission thereis necessarily a drop of temperature between the active electronemitting surface and the heating element, with the result that to obtainthe same temperature of the active emitting material as is obtained inthe directly heated or filament type of cathode it is necessary toemploy current of substantially greater intensity, other conditionsbeing the same. This necessity for large current is further enhanced bythe fact that much greater radiating surface and mass is had in theindirect heated method of construction, requiring much larger quantityof heat to maintain the active surface at the desired temperature. Thelarger current results in the production of more intensiveelectromagnetic and electrostatic fields within the interior regions ofthe tube where they are best located to have large effect on theoperation of the tube. Since the alternating current of usual housesupply systems is of such frequency as to be within the range of theuseful frequencies of desired signal currents being handled by the tubesit is not feasible to eliminate the disturbances after they have beencreated, this because any attempt at such elimination results ineliminating some of the desired signal currents. It is therefore betterto prevent the creation of the disturbances than to permit theircreation with the hope of later elimination.

It is obviously most desirable to be able to heat the cathodes of tubesat potentials directly available from ordinary commercial current supplysystems, as such supply systems are now more or less standardized in thematter of supply potentials, and such practice avoids the interpositionof converting apparatus, such as transformers, rectifiers, filters andthe like. There is also the advantage that the supply of current at highpotentials involves the use of currents of small intensities, thuseliminating the necessity for maintaining supply wires short and oflarge cross section.

The diiilculty of using heating current at high potential is thenecessity for crowding into the very small space usually available in atube the necessary length of fine wire, and preventing in such crowdingshort circuits and other forms of current leakage. Also the increasedelectrostatic field intensities produced by the higher differences ofpotential are troublesome. This invention makes special provision forovercoming these difficulties.

High potentials in gas filled tubes oifer particularly difilcultsituations at those parts of the leads carrying the high potentialcurrents through gas filled portionsof the tube, because such gasfacilitates the production of ionic discharges between high potentialpoints, and such discharge is almost certain to result in immediatedestruction of the more or less fragile lead-in or heating wires.

The invention is further explained in connection with the figures of theaccompanying drawing, in which-like reference characters in the severalfigures represent like parts as far as possible.

Fig. 1 shows a cathode organization of the indirect heated typeparticularly suitable for heating current supplied at low potentials.

Fig. 2 shows a cathode organization within a suitable container orvessel in which special provision is made for obtaining indirect heatingwith current supplied at higher potentials.

Fig. 2a illustrates in detail several of the features of Fig. 2.

Fig. 3 shows a special arrangement of the cathode organization makingprovision for use in gas filled tubes.

Referring to Fig. 1 there is shown the usual glass stem S of a dischargetube, which acts as a carrier of the lead-in wires and a support for themultiple electrode organization. There is shown the usual cylindricalanode or plate P surrounding control electrode or grid G. The cathodestructure is shown to include a thimble or cylindrical core 0 forcarrying the emitting g i A coating. It is not necessary for the thimbleto be cylindrical, as other cross sectional forms may have advantagesunder particular circumstances. The thimble is shown supported by a 5suitable upright W with horizontal extension, this upright makingconductive and supporting con-' tact with the metallic thimble at O. Theupright W is conductive and connected to a lead-in wire through the stemS.

The thimble may be made of any one of the.

usual core materials for electron emitting oxides or compounds, such asplatinum, molybdenum, nickel, cobaltum or alloys of them or withaluminium. Since no particular structural strength is required of thethimble, as is usually the case with directly heated cathodes, some ofthe softer metals, such as nickel and cobalt, may be employed withadvantage, and are particularly suitable because they are not subject tocorrosive disintegration to the same extent as some of the other metals.While the matter of disintegration of the metal of a comparatively largethimble is not so serious as the disintegration of the core of afilament in the directly heated type of cathode, on the other hand inmany cases the corrosive compounds formed by the corrosive materialshave the effect of lessening the electron emission of the cathode.

The heater system is shown to include a pair of wires H helicallytwisted or helically wound about each other, and conductivelycross-connected at the top and connected to the suspension point 0, andtherefore to supporting upright W, the two lower ends of this helicallytwisted arrangement being connected to lead-in wires of the stem S. Thishelically twisted arrangement requires that the two wires be effectivelyinsulated one from the other to prevent undesirable leakage. Since thesewires must be heated to 40 temperatures higher than the requiredtemperature at the surface of the thimble, even to the extent of severalhundred degrees, and therefore operate at rather high temperatures, forinstance, in the neighborhood of 1000? C., the problem,

when an insulating coating is desired, of insulating one from the otherin the presence of this high temperature becomes a special one. I havefound that certain compounds such as beryllium oxide and aluminium whichdo not have high electron emission, when mixed with sintering materials,such as the fluorides, for example, strontium fluoride, form admirableinsulating coatings for such twisted wires operating at the hightemperatures required.

Previous attempts to accomplish similar results, using the silicates andlike materials which are non-conducting at low temperatures, haveresulted in practical failures at the high temperatures involved.

The heating wires may be nickel, tungsten or like materials having thedesired resistance characteristics, and which will withstand the hightemperatures involved, and more particularly those adapted to receiveand hold the chemical compounds involved in the insulating coating. Itis desirable that the core material not be one that forms a corrosivecompound with the coating material. It is possible to avoid thissituation by plating such a core with a metal not subject to suchcorrosive compound formation.

The coating compounds, or other compounds mentioned, may be formed onthe heating wire as coatings by processes now well known for theformation of such coatings.

It is thus seen that if the two ex e nal l ads of the helically twistedheating wire H be connected to an alternating current transformer,whereby the heating system is supplied with alternating current, thatthe connection to the heating Wire of the upright W at point 0 providesa connection to the neutral potential point of the heating wire H, andfurthermore provides a connection to the most neutral potential point inthe cathode thimble, so that such arrangement makes an ideal connectionbetween the grid circuit and the cathode system to avoid introducingvarying potential effects on the grid by reason of such alternatingcurrent use. It will further be noted that the connection between theheater wire and the cathode thimble is very short, and therefore ofnegligible resistance, thus substantially eliminating a potentialdifference between these two elements. It is preferable to form thecathode thimble of one continuous cylindrical body rather than having anarrangement of spiral wires or ribbons, this because extremely lowresistance is maintained between the neutral point of the thimble anddistributed points in the thimble surface, to maintain low differencesof potentials between such points.

It will also be noted that the metallic thimble completely surrounds thealternating current carrying heater wires, this including a completeclosure of the top of the thimble, so that the electromagnetic andelectrostatic fields are shielded from the regions outside of thethimble to a high degree. It is also to be noted that by reason of thetwisted formation of the heated wires that the resultant fields aremaintained extremely low, so that any fields straying from the interiorregion of the thimble are naturally weak, resulting as they do from aweak resultant field.

It is desirable to coat with electron emitting material only thatportion of the thimble included within the extent of the grid, or evento have the grid structure extended slightly beyond the limits of thecoating. Another feature worthy of attention is to extend the lower partof the thimble, which is open in the direction of the stem, somewhatbelow the lower extent of the grid structure, this in order to shield asfar as possible the grid from the potentials on the lead-in wires of theheater system.

In Fig. 2 modifications are made which particularly adapt the heatingarrangement and cathode system for energizing from a high voltagesource, either direct current or alternat ing current, such as theordinary volt light socket, and therefore without the use of the usualstep-down transformer for alternating current operation. In this casethe heating wire H comprises closely helically wound fine wire wound inbifilar form in two helically ascending parts in the grooves of agrooved sleeve B, shown in detail in Fig. 2a, each part having aconnection to a leading in wire in the stem S, the details of thewinding being better shown in Fig. 3. The two parts are electricallycontinuous one to the other, and may be conductively connected at thetop mid point, and therefore the alternating current neutral point, tothe thimble C and conductive support W which passes through the groovedsleeve to a leading in wire E (Fig. 2a) in the stem S. If the ultimatetube is intended for operation by filament heating directly from acommercial lighting and power system it is not advisable to connect themid point of the heating wire to the wire W because such systems areusually grounded on one side, and any use of the tube in a systemrequiring grounding of the wire W would result in a seriousshort-circuit. The cathode or thimble C is however connected to supportW at the point as shown.

The sleeve B must be an insulating material capable of remaininginsulating at the very high temperatures mentioned in connection withinsulating features in Fig. 1. I have found that such mixtures asberyllium oxide, thorium oxide, aluminium oxide, together with sinteringmatel0 rials, such as fluorides like barium fluoride and calciumfluoride, one such mixture bearing-the commercial name steatite, areparticularly suited for forming such an insulating sleeve.

One suitable method of making such a sleeve is to place powders of thesematerials in a pressure mould having the desired groove formation,- thesupport W being passed through the center of the mould. After formationof the ingot by pressure it can then be heated to sufllcient temperatureto sinter the materials into a hard mass. The sleeve may have anenlarged portion D of such size to fit snugly within the lower part ofthe thimble C, with holes K, K as shown through which the two ends ofthe heater wire may pass to the lead-in wires of stem S, shown in detailin Fig. 2a.

The support W serves as a connection to the neutral point of cathode Cand, if desired, as a connection to the neutral point of the heatingwire system. It also acts to support the heating wire, the heating wireinsulator, and the cathode thimble, and at the same time spaces thethimble for proper relation to the enlarged portion D on sleeve B.

In view of the extremely restricted space available within the cathodethimble of an ordinary tube the length of wire required to satisfy thehigh potential contemplated for the heater and give the required heatingsurface is obtained by 40 winding helically wound flne wire in ascendinghelical form, and two such ascending helices are used, wound bifllarside-by-side in the same direction, in order to produce the fieldneutralizing effects described in connection with the helically 15twisted form of heater of Fig. l and to bring the neutral point of theheater system adjacent the neutral point 0 of the thimble C.

It is particularly desirable to have the turns of the helices of thefine wire closely spaced in order to secure great length of wire in thesmall space available. Since winding a closely spaced helically woundwire on a sleeve would unquestionably result in there being manycontacts between turns at the inner side of such winding, it isnecessary to coat such a wire with an insulating coating as in the caseand under the conditions of the heating wire of Fig. 1. The voltagebetween the adjacent turns of the spiral is low, so that a coating ofthis kind is not called upon to insulate against high potentials. Thehigh potentials between the parts of. the heater system are taken careof by winding in the spaced grooves of the insulating sleeve.

It is apparent that the end of the cathode systern towards the stem issubject to greater heat loss by conduction than the removed end, so thatunless special provision is made the cathode will not have uniformelectron emission temperature throughout. If arrangement is made to heatthe lower part of the system at a. higher rate this effeet can beovercome. One way of accomplishing the result is, in winding thehelically wound wire, to stretch it in ascending so'that the turns aregradually more widely spaced; or the slope of the helices on the sleevecan be gradually increased in ascending. I have found another eifectwhich may also be employed usefully in this direction, which is usingfor the coating a compound that emits electrons, such as strontiumnlckelate, thus producing electron currents between the two parts of thehelical windings, which electron currents will be more intense at thestem end than the upper end because of a higher difference of potentialat the stem end. These electron currents will increase the generalheating current to make the total heating effect greater at the higherheat loss end.

It is thus seen that the arrangement of Fig. 2 provides for reducing thehum producing effects in like way to Fm. 1, except with the improvementthat the connection to the neutral point is led directly through themiddle of the heater winding instead of outside, as in Fig. 1, thussecuring the best possible location for neutralizing the alternatingcurrent fields, and including those of the lead-in wire connections inthe stem. This is particularly important in the case of the high heatingpotentials contemplated. Since the support wire W, passing through themiddle, is conductively connected to the surrounding thimble C, both ofwhich are of low resistance, an ideal shield organization is providedfor, especially in the matter of reducing thimble eddy current voltages.v

Fig. 3 includes features particularly directed towards permitting highpotential heating current in gas-filled tubes, it being the object toprevent ionic discharges between parts of the heater system as suchdischarges, if permitted,

will result in almost immediate destruction of the fine wires employedby reason of the impact energy of ions. The likelihood of such dischargeis increased if electron emitting coatirm material is used in theinsulating coating of the heater wire as such'discharges can then beproduced at much lower differences of potential.

In tubes using quite low gas pressures the prevention of discharge canbe had in whole or in part by spacing the difierence of potential partssuillciently short distances that they are about equal to the mean freewavelength path of the electrons for the particular gas and pressure ofit used. Such spacing will usually not be effective in gas-filled tubesfor the spiralled part of the heater because usually the distancesbecome too small for practical construction, but may be of particularvalue in spacing the lead-in wires. For higher pressure gas-filledtubes, where physical spacing is not practical, it becomes necessary toresort to other expedients. I provide an arrangement for preventingionic discharges by surrounding the diiference of potential parts withpowders or materials eilfective to prevent ionic discharges taking placethrough them, such aspowders of the same materials previously mentinnedfor both the coatings of the heater wires and forming the insulatingsleeve B. These powders T, Fig. 3, are so inserted inside the thimble Cas to closely surround the parts to be protected, and when the tube isheated these powders form in whole or in part the compounds previouslymentioned, and therefore give suificient non-com ductivity forelectrical current to prevent short circuits or leaks of undesireddegree between the difference of potential parts. On the other handthese compounds have a sufilciently high heat conductivity to permit oftransferring the desired quantities of heat to the thimble C withoutrequiring a too high temperature of the heater system. i

In order to extend this protection to the leadin wires there is providedon the stem 8 a mounting M through which the lead-in wires pass asshown. This mounting may be made of the 5 same material as the sleeve B,and should have means for making a flange or other suitable joint withthe thimble C as shown, thus forming with V the thimble C a chambercompletely filled with the desired material. This mounting at the sametime serves to center the whole cathode structure. It is not necessaryfor the joint between the mounting M and thimble C to be a gas tightJoint, as the filling takes care of the presence of any gas. After thethimble C is in place the connec- 5 tion with the support wire W is madeby fusing or other means, so that the support wire then serves to holdthe arrangement as a compact unit. If tubes of large outputs arecontemplated for use with alternating current as a source of cathodeheating the troublesome field effects due to increased intensities ofcurrents required may be further reduced by including in the tube, suchas Fig. 2, two lead-in stems S at opposite ends, and

bringing the grid and plate leads through one stem and the heatingcurrent leads through the other stem. The grid and plate leads are, inthis way, widely separated from the heater leads carrying the heavyheating alternating currents.

Having thus described my invention, what I claim is:

1. A cathode organization including a current carrying-heating element,a metallic support for an electron emitting coating closely surroundingsaid heating element, and a filler of effectively electricalnon-conducting material at the operating high temperatures of saidorganization in the normally free spaces internally of said support,said filler containing an electron emissive compound in close proximityto points of maxi- 0 mum heat energy loss whereby the said metallicsupport is uniformly heated throughout its length.

2. A discharge tube having a cathode organization including a hollowmetallic support for an external electron emitting coating, an electrodemounting stem in said tube, a conductive support erected in saidmounting stem in conductive continuation'or alead-in wire, and passingcentrally through said hollow coating support to a conductive andsupporting connection therewith, O and a bifilar system of heatingconductors in sulatedly wound about said conductive support.

3. In a discharge tube, the combination of a stem, lead-in wires throughsaid stem, an electrode support carried by said stem and in conductivecontinuation of one of said lead-in wires, a cathode thimble carried byand surrounding said support, a cathode heater within said thimble, andmeans for spacing said heater element from said support and saidthimble.

4. In a discharge tube, the combination of a stem, lead-in wires throughsaid stem, a cathode support carried by said stem and in conductivecontinuation of one of said lead-in wires, an insulating elementsurrounding said support, a cathode heater element carried by saidinsulating cathode heater element consisting of a bifilar helicalwinding of wire carried by said insulating element and in conductiveextension of a pair of said lead-in wires, a cathode thimbleconductively mounted upon said support and surrounding said heaterelement, and means for spacing said heater element from said thimble.

6. In a discharge tube, the combination of a stem, lead-in wires throughsaid stem, a cathode support carried by said stem and in conductivecontinuation of one of said lead-in wires, an insulating elementsurrounding said support, a cathode heater element consisting of abifilar winding of helically wound wire carried by said insulatingelement and in conductive extension of a pair of said lead-in wires, acathode thimble conductively mounted upon said support and surroundingsaid heater element, and means for spacing said heater element from saidthimble.

7. A cathode organization including a current carrying heating element,a metallic support for an electron emitting coating closely surroundingsaid heating element, and a filler of beryllium oxide in the normallyfree spaces internally of said support. I

8. In a discharge tube having an indirectly heated cathode, a heatertherefor having a noninductive bifilar helical winding of helicallywound wire, said wire being coated with beryllium oxide.

9. In a discharge tube having an indirectly heated cathode, a heatertherefor comprising an insulating support, and a pair of helicalwindings of helically wound wire wound about said insulating support andhaving the turns of said windings disposed in grooves in said support.

10. A cathode organization comprising a twisted pair of conductorshaving an insulated coating forming a heating element, the coatedconductors being in physical contact and connected together at one end,and a support for an electron emissive coating surrounding said heatingelement.

11. In an electron-discharge device, a cathode comprising a helicallywound type of heater filament supported along its length by a refractorysupporting element of insulating material, said refractory elementextending beyond the vicinity of said heater filament, electron-emissivemeans surrounding said heater filament, and means for supporting saidrefractory element at a point substantially removed from said filament,said electron-emissive means and said refractory supporting elementbeing rigidly supported with respect to each other at one end while theyare so supported at the other end with respect to each other as topermit relative movement caused by expansion.

12. In a discharge tube having an indirectly heated cathode, a heatertherefor having a noninductive bifilar helical winding of helicallywound wire, said wire being coated with a layer of strontium nickelate.

13. An electron tube of the auxiliary heater type having an electronemitter comprising a filament disposed within grid and plate electrodesconsisting of a pair of spiralled sections disposed parallel one toanother and having the magnetic fields thereof confined substantiallywithin the central zone of said electron tube, means surrounding saidfilament includingelectron emitting surfaces specially related to saidfilament for substantially eleetromagnetically shielding said grid andplate electrodes from the field around said filament and supportsadjacent each end of said means for fixing the spacial relation of saidmeans with respect to said filament.

14. A cathode structure comprising a hollow elongated member having anexternal surface adapted to emit electrons upon heating, a heatingfilament within said member, said filament comprising twoseries-connected, helical portions, the terminals of said filamentextending from one end of said hollow member and the respective 10convolutions of the two helical portions lying in substantially the samecircumferential plane in relative parallel spaced relationship, meansclosing one end of said hollow member, said means carrying a rod-shapedinsulating member, at least one turn of each of said helical portionsclosely surrounding and engaging the surface of said rod-shaped member,whereby all the turns of each helical portion are held spaced from eachother, an unobstructed annular space being pro- 20 vided within theinner walls of said hollow membeer and said filament, whereby said wallsmay be heated by direct radiation from said filament, said structureincluding means for closing the opposite end'of said hollow member.

15. A cathode structure comprising a hollow elongated metal memberhaving an external surface adapted to emit electrons upon heating, aninsulating plug closing one end of said hollow member, a heatingfilament within said member,

:10 said filament comprising two series-connected helical portions, theterminals of said filament extending from one end of said hollow memberand the respective convolutions of the two helical portions lying insubstantially the same cir- 35 cumferential plane-in relative parallelspaced relationship, said plug carrying a rod-shaped insulating memberextending part way toward the other end of said hollow member, at leastone turn of each of said helical portions closely sur- 40 rounding andengaging the surface of said rodshaped member, whereby all of the turnsof each helical portion are held spaced from each other, an unobstructedannular space being provided between the inner walls of said hollowmember 45 and said filament, whereby said walls may be heated by directradiation from said filament.

16. A cathode structure comprising a hollow elongated member having anexternal surface adapted to emit electrons upon heating, a heat- .70 ingfilament within said member, said filament comprising twoseries-connected helical portions, the. terminals of said filamentextending from one end of said hollow member and the respectiveconvolutions of the two helical portions lying in 5.3 substantially thesame circumferential plane in relative parallel spaced relationship,means closing one end of said hollow member, said means carrying arod-shaped insulating member, at least one turn of each of said helicalportions closely to surrounding and engaging the surface of saidrodshaped member, whereby all the turns of each helical portion are heldspaced from each other, an unobstructed annular space being providedwithin the inner walls of said hollow member and said filament, wherebysaid walls may be heated by direct radiation from said filament, andmeans for closing the opposite end of said hollow member.

17. An electron emitting cathode of the indi- 70 rectly heated typecomprising a tubular metal sleeve member exteriorly coated withthermionically active material and an interlorly positioned doublehelical heater element electrically insulated therefrom, the terminalsof said coll ex- 75 tending from one end thereof and the respectiveconvolutions of the two helices lying in substantially the samecircumferential plane in relative parallel spaced relationship, a smallrod solely of insulating material extending from said one end of saidtubular metal sleeve partway toward the other end of said tubular metalsleeve, at least one turn of each of said helices closely surroundingand engaging the surface of said rod, whereby all of the turns of eachhelix are held spaced from each other, an unobstructed annular spacebeing provided between the inner walls of said hollow member and saidheater, whereby said walls may be heated by direct radiation from saidheater.

. 18. A cathode organization comprising a heater element having parallelconductors electrically continuous at one end, an insulating coatingthereon, the conductors being twisted about each other so closely thatthe over-all diameter of said heater element is only slightly largerthan the sum of the coated conductor diameters, and a metallic cathodesleeve surrounding said heater and spaced therefrom, said sleeve havinga thin wall relative to its diameter.

19. In a grid-controlled discharge tube, a cathode organizationcomprising a cathode sleeve having an outer emissive surface and a thinmetal wall pervious to magnetic fields, a heater element disposed incentral spaced relation within said sleeve and adapted to heat thesleeve by direct radiation and thereby heat the cathode surface toemissivity with low heater voltage compared to the usual supplyvoltages, said heater being formed of two parallel conductors closelvtwisted about each other in insulated relation and electricallycontinuous at one end, and a control grid adapted to control theelectron emission from said emissive surface.

20. A cathode heater comprising a helical winding and an insulatingsupport therefor having the rigidity and refractoriness to support theturns of said winding in insulated spaced relation at a temperature of1000 degrees centigrade, said support being composed substantially of asintered mixture of metallic oxide selected from the oxides ofberyllium, thorium and aluminium, and a sintering material.

21. In a thermionic tube of the heater type a tubular cathode, a heaterfilament within said cathode, means to support the two ends of saidfilament, and means integral with said filament to insulate saidfilament from itself and from said cathode, said means comprising acoating containing as an essential element crystalline aluminum oxideintegrally formed on a refractory base heater.

22. In a thermionic tube of the heater type, a tubular cathode, a heaterfilament within said cathode, means to support the two ends of saidfilament and means integral with said filament to insulate said filamentfrom itself and from said cathode, said means comprising a. coatingcontaining as an essential element beryllium oxide integrally formed ona refractory base heater.

23. An electric discharge tube filament comprising a refractory metalbase having an insulating coating thereon containing beryllium oxide asan essential element.

24. A heater cathode unit for electric discharge tubes comprising arefractory heater filament, a cathode positioned to be heated by saidfilament and an insulating body between said cathode and heater composedof beryllium oxide mixed with a sintering material.

25..A vacuum tube filament comprising a re- Iractory metal base havingan insulating coating composed substantially oi beryllium oxide and asintering material, said coating being integral with said base.

26. A filament for electric discharge tubes comprising a base oftungsten having an insulating coating containing beryllium oxide and asintering material.

27, A refractory filamentary metal heating element for an electron tubehaving a coating comprising a mixture composed of an oxide of an elementoi the class comprising aluminum and beryllium and a sintering materialselected irom the group 01' compounds consisting of fluorides of barium,strontium and calcium, and steatite.

CARL J. R. H. you WEDEL.

